The effects of harvesting Pacific hake (Merluccius productus)
were examined with a multi-species numerical model composed of
seven logistic growth equations coupled by a food web. The
food web was composed of: California sea lions (Zalophus
californianus), hake, sablefish (Anaplopoma fimbria), spiny
dogfish (Squalus acanthias), a generic rockfish species
(Sebastes spp.), Northern anchovy (Engraulis mordax), and a
generic euphausiid species (as an example, Pacific krill,
Euphausia pacifica). The model was tuned to mimic stock
assessment biomass estimates for the years 1980 to 1991, after
which a short term experiment and a sensitivity analysis were
conducted. The short term experiment used a factorial design,
with hake fishing and fishing for rockfish, sablefish, and
anchovy as treatments. It was analyzed with scale analysis
techniques. The results indicate that hake (from a management
viewpoint) is potentially most important in the offshore
community as a prey item for sea lions and as a predator on
anchovies, but hake fishing mortality had a small effect on
either population during the time span of the experiment.
Results also suggest that hake has little or no competitive
interaction with other species that are trophically similar.
Increased harvesting of hake would probably do little to
increase the biomass of rockfish or sablefish. The general
conclusion of both the sensitivity analysis and the experiment
is that species below their carrying capacity are mostly
affected by changes in growth and removal processes while
species close to their carrying capacity are mostly affected
by processes controlling prey availability.
A forty year projection from 1991 to 2031 was conducted
to examine the effects of hake fishing on sea lion and anchovy
biomass. Results indicate that sea lion biomass will vary
inversely with hake fishing effort, while anchovy biomass is
directly proportional to hake fishing effort. Results also
indicate that hake experience environmental conditions not
favorable to recruitment. During favorable conditions the hake
population builds up a "surplus" that carries it through
periods of unfavorable conditions. Increased hake fishing
effort reduces the response of the population to favorable
conditions. The results of this research constitute a step
from the theory toward the practice of proactive multi-species
and ecosystem management. / Graduation date: 1995
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32128 |
| Date | 05 December 1994 |
| Creators | Gartz, Russell G. |
| Contributors | Sampson, David B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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